The invention relates to a method for conveying electrically conductive paints from a supply system at ground potential, especially a color changer, to a consumer at high voltage, especially an electrostatic paint atomizer.
The electrostatic processing of electrically highly conductive paints, for example water-based paints, makes it necessary to transfer the paint from ground potential to high voltage potential, it being necessary to ensure electrical isolation between the potentials.
For this purpose, various procedures are known and described, for example in U.S. Pat. No. 5,632,816 or DE 197 56 488, where operations are carried out with a paint supply lance which is moved into the paint discharge position through an insulating liquid.
The common factor in the known methods is that they either require very complex control or monitoring functions or cannot be used in connection with automatic quick color-change systems.
Accordingly, the invention is based on the object of providing a simply structured method which requires comparatively low outlay on control and is also suitable for automatic quick color-change systems.
According to the invention, this object is achieved by individual quantities of paint being divided off and moved at intervals in space and time along a conveying path between the supply system and the consumer, the length of the conveying path exceeding the extent of the individual quantities of paint in the conveying direction by an amount that is sufficient as an isolating path.
The invention also relates to an apparatus for implementing this method, having a conveying line for paint, which is connected into the connection between a grounded supply system, especially a color changer, and a consumer at high voltage, especially an electrostatic atomizer.
To this extent, also, the abovementioned object of the invention applies, namely to provide an apparatus which is constructed comparatively simply, manages with a low outlay on control and can also be used for automatic quick color-change systems.
According to the invention, this apparatus is defined by the fact that the conveying line consists of an insulating material, there are arranged in the conveying line at least one pair of pigs comprising a rear pig and a front pig, the rear end of the conveying line is assigned a loading station for supplying divided-off quantities of paint between the two pigs, the front end of the conveying line is assigned a discharge station for removing the divided-off quantities of paint from the conveying line, a transport device is provided to displace the pair of pigs with an accommodated quantity of paint from the loading station to the discharge station, and a reverse transport device to displace the pair of pigs from the discharge station to the loading station, the length of the conveying line between the loading station and the discharge station and the length of the unit quantities of paint accommodated between the pigs are dimensioned such that the added conveying-line sections upstream and downstream of the unit quantities of paint always form an isolating path of sufficient length between the loading station and the discharge station.
According to the invention, therefore, the paint is conveyed discontinuously in individual quantities, the longitudinal extent, measured in the conveying direction, of the individual units of paint being considerably below the length of the conveying path or the isolating conveying line, so that a sufficient isolating path always remains within the latter. Because of this measure, the individual quantities of paint or units of paint can be transported without difficulty into the high voltage area, for example by means of compressed air or an insulating liquid as a thrust medium, as outlined below using the exemplary embodiment. Since dividing up the quantities of paint does not raise any difficulties either, the method according to the invention and the associated apparatus prove to be fit for the purpose, simple and operationally reliable.
The discontinuous transfer of the individual quantities of paint presupposes at least partial intermediate storage of the paint in the high voltage area, if the consumer is to be supplied continuously. However, such intermediate storage can be avoided if, according to a particularly expedient version, the divided-off quantities of paint are supplied via two conveying paths or through two parallel conveying lines, the discharge of paint being carried out without interruption alternately from the quantities of paint from the one conveying path or conveying line and the other.